This invention relates generally to a finger operated liquid dispensing pump of the hand-held variety; and more particularly to such a pump having an improved discharge valve. Additional features include means for selectively locking the plunger in a fully depressed position and means for selectively immobilizing the pump plunger in a fully raised position.
Dispensers of the general class to which the present invention is directed have included discharge valving in the form of annular flaps or sleeves which are resiliently flexible for opening the discharge passage in response to an axial flow of pressurized liquid applied during the plunger pressure stroke. The discharge passages normally open as the flap bends or flexes radially inwardly, or the sealing flange or sleeve expands circumferentially in response to positive pressure. In either case, the hoop ring forces at the circular edges of such valves must be overcome for opening the discharge. However, it is difficult to predict and devise an appropriate hoop strength which must be overcome for the dispensing of different products having different flow characteristics. Moreover, these known valves rely on their inherent resiliency which self biases the circular sealing edge against the valve seat for controlling the discharge passage. Thus, it is most difficult if not impossible to adjust this self biased pressure to control the loading of the valve, without substituting a different valve flap or sleeve.
Moreover, different approaches have been taken for immobilizing the plunger during a non-use condition of shipping and/or storage. One such approach is disclosed in U.S. Pat. No. 3,527,551 for locking the plunger in a fully depressed position as lugs on the outside of the plunger engage beneath lips projecting inwardly from a housing in which the plunger reciprocates. Lock-down is effected upon rotation of the plunger after it is fully depressed. It would, however, be desireable to provide a more positive plunger lock-down to avoid any inadvertant unlocking of the plunger while at the same time effecting a positive seal against leakage of product from the container through the container vent opening during plunger lock-down.
Other approaches have been taken, including that disclosed in the aforementioned related application, for immobilizing the plunger in a fully raised position above the pump body.